The present invention relates to a method of removing the generator rotor from an aligned gas turbine-generator-steam turbine configuration for maintenance and returning the generator to useful service in the aligned gas turbine-generator-steam turbine configuration.
A gas turbine, generator and steam turbine are typically axially aligned one with the other with the generator located between the gas and steam turbines whereby the turbines drive the generator rotor to produce electrical power. This configuration is known as a STAG (steam and gas) combined-cycle system. In the STAG combined-cycle system, it will be appreciated that the opposite ends of the generator are mechanically coupled to the gas and steam turbines, respectively. The components of these systems are generally mounted on foundations prepared for supporting these large system components. Typically, the generator rotor, i.e., the generator field, must be removed from the generator for scheduled maintenance or repair. With the three main components of the combined-cycle system secured to the foundation, however, and in axial alignment one with the other, it is not possible to remove the generator field axially due to the lack of clearance with respect to the turbines at opposite ends of the generator. Maintenance on the gas and steam turbines can typically be performed in situ because the turbine housings are split along a horizontal midline enabling removal of each upper casing the exposed rotors of the gas and steam turbines. This leaves the lower turbine casings resting on the foundation. However, because the generator is an electromagnetic component, it is not possible to split the generator rotor and casing at the centerline and lift the generator rotor from the generator in a vertical direction.
Prior maintenance has been performed on generator rotors in combined-cycle systems, primarily in two ways. Once the generators are mechanically uncoupled from the turbines, the generators are directly lifted from the foundation and moved to a laydown area in the plant where rotor removal in an axial direction is not hindered by the presence of other equipment. Heavy-duty lifting equipment typically on-site is used to perform that process. Another prior process for maintaining generator rotors requires a movable slab forming part of the foundation for the generator. With the generator located on the movable slab, the generator may be displaced transversely or laterally from between the turbines and thus moved to a position where the turbines do not interfere with axial removal of the generator field. See, for example, U.S. Pat. No. 5,701,731.